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Movements, leaders, victories and the continuing fight for equality.
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THE BHP WIRE —
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Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
Innovation, patents, science, technology and world-changing contributions.
Pioneers, champions, Negro Leagues, records, activism and excellence.
Meet the people whose lives, choices and achievements shaped the journey.
Black towns, communities, institutions and places where history happened.
Moments that changed communities, movements, institutions and the nation.
Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
| Heliozoa | |
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| Heliozoan depicted by Louis Joblot, 1718 | |
Scientific classification
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| Domain: | Eukaryota |
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Plus select genera in other orders (see text) | |
Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (axopodia) radiating from their spherical bodies, which are responsible for their common name.[1][2][3] The axopodia are microtubule-supported projections from the amoeboid cell body, and are variously used for capturing food, sensation, movement, and attachment. They are similar to Radiolaria, but they are distinguished from them by lacking central capsules and other complex skeletal elements, although some produce simple scales and spines.[4] They may be found in both freshwater and marine environments.
Originally the heliozoa were treated together as a formal taxon Heliozoa or Heliozoea, with the rank of class or phylum, but it has been realised that they are polyphyletic, as the various orders show notable differences and are no longer believed to be descended from a single common ancestor. Instead, "heliozoa" is regarded as a descriptive term applying to various lines of protists.
The primary groups include:[5]
Several nucleariids were once considered heliozoa, but they do not have microtubule-supported axopods and so are now considered filose amoeboids instead.
In 2012, Cavalier-Smith proposed maintaining the name Heliozoa as a formal taxon by reducing it to only centrohelids, which are the most species-abundant group of heliozoa to date. He established a new phylum Heliozoa emended to include only two classes: Centrohelea, the centrohelids; and Endohelea, a smaller group containing only the genera Heliomorpha and Microheliella.[7] This was short-lived, however, because later the same author transferred Centrohelea to the phylum Haptista and Endohelea to the phylum Cryptista, making his phylum Heliozoa polyphyletic once more. From 2015 onwards, he proposed yet another definition for Heliozoa, exclusively as a monotypic subphylum of Haptista containing only the class Centrohelea.[8] This renewed circumscription never reached consensus, and Heliozoa continues to be used in the same regard as the traditional, polyphyletic category including amoebae other than centrohelids.[9][10][11]
The heliozoa are a polyphyletic grouping of various protists that have independently evolved axopodial arms. Some of the heliozoan groups are intermingled in the supergroup Rhizaria with radiolarians, their mostly marine counterpart.[5]
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule-supported projections from the amoeboid cell body, and are variously used for capturing food, sensation, movement, and attachment. They are similar to Radiolaria, but they are distinguished from them by lacking central capsules and other complex skeletal elements, although some produce simple scales and spines. They may be found in both freshwater and marine environments.
The actinophryids are an order of heliozoa, a polyphyletic array of amoebae. They are common in fresh water and occasionally found in marine and soil habitats. Actinophryids are unicellular and roughly spherical in shape, with many axopodia that radiate outward from the cell body. Axopodia are a type of pseudopodia that are supported by hundreds of microtubules arranged in interlocking spirals and forming a needle-like internal structure or axoneme. Small granules, extrusomes, that lie under the membrane of the body and axopodia capture flagellates, ciliates and small metazoa that make contact with the arms.
The stramenopiles, also called heterokonts, are protists distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cell surface, and in some they have been secondarily lost (in which case relatedness to stramenopile ancestors is evident from other shared cytological features or from genetic similarity). Stramenopiles represent one of the three major clades in the SAR supergroup, along with Alveolata and Rhizaria. Stramenopiles are eukaryotes; most are single-celled, but some are multicellular including some large seaweeds, the brown algae. The group includes a variety of algal protists, heterotrophic flagellates, opalines and closely related proteromonad flagellates (all endobionts in other organisms); the actinophryid Heliozoa, and oomycetes. The tripartite hairs characteristic of the group have been lost in some of the included taxa – for example in most diatoms. Many stramenopiles are unicellular flagellates, and most others produce flagellated cells at some point in their lifecycles, for instance as gametes or zoospores. Most flagellated heterokonts have two flagella; the anterior flagellum has one or two rows of stiff hairs or mastigonemes, and the posterior flagellum is without such embellishments, being smooth, usually shorter, or in a few cases not projecting from the cell. The term 'heterokont' has been used both as an adjective, indicating that a cell has two dissimilar flagella, and in the name of a taxon. The groups included in that taxon have however varied widely, creating the 'heterokont problem', now resolved by the definition of the stramenopiles.
The centrohelids or centroheliozoa are a group of heliozoan protists, single-celled eukaryotes with stiff radiating arms (known as axopodia) supported by microtubules and bearing extrusomes (known as kinetocysts). Their cells are spherical, ranging from 3 to 150 μm. Unlike other heliozoa, centrohelids lack flagella, have flat ribbon-shaped mitochondrial cristae, and arrange their microtubules in hexagons or triangles. Their microtubule-generating organelle, the centroplast, has a unique shape with a central trilamellar disc surrounded by two hemispherical caps. Some are naked or covered in a mucous coat, but most centrohelids produce cell coverings, namely organic spicules and siliceous scales of various species-specific shapes. Several species form colonies. Centrohelids are passive predators with a cosmopolitan distribution. They feed on bacteria, other protists, and invertebrate larvae by phagocytosis; they can merge several cells around a larger prey to ingest it. Although they have been studied in aquatic (mostly freshwater) environments, they are more diverse in soil habitats. They include both free-floating and benthic forms, some of which attach to the substrate by a stalk. Centrohelids are the closest relatives of the haptophyte algae, together forming the clade Haptista. Both groups have mineralized scales and at least one thin microtubule-based appendage. The common ancestor of centrohelids lost flagella and probably produced the two known types of cell coverings, organic spicules and complex siliceous scales. Some species can still produce both, while others secondarily lost or simplified them. Centrohelids compose the class Centroplasthelida, in reference to their centroplast. Around 130 species have been described, but they only represent about 10% of the total estimated diversity, according to environmental DNA surveys. They are classified in 11 families grouped into two major clades, Pterocystida and Panacanthocystida.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Shirley Chisholm, elected in 1968.
